No, it'd still be "100".. Admin numbers have three digits.. IIRC, the anti-sub sqn (VS) in a carrier air wing has six-eight S-3s assigned... So if the CAG was a Viking driver, he'd be flying "Showtime 100" still..
The USAF does it a little different.. They generally use separate callsign prefixes that have a common theme, like birds or cars or something.. A squadron of fighters might be "Pintail", with the subordinate elements of the sqn being "Pekin", "Mallard", and "Drake", or cars, like "Ford", "Chevy", and "Dodge" with each flight having the same numbers, "One" (or "Lead", and "Two" (Flight Leader and his wingman) and the second element leader being "Three", and his wingman, "Four..
When say, the Squadron is using "Pintail", the squadron leader will call, "Pintail Check" and hear back from his element leads call back, Pekin"-"Mallard"-"Drake".. Then, when say, the "Mallard Flight" Leader calls, "Mallard Check", he'll hear, in quick sucession, "Two"-"Three"- "Four"...
As far as pilots chatting back and forth, using their personal callsigns, that only happens in the movies and in units where radio discipline has gone to hell, but in the heat of the moment, when they're in a big furball, it's quite possible that some will actually call out a personal callsign..